I must admit my D800 seems to attract more dust and needs more cleaning than my D700 did or D7000 does. This week I had a stubborn sensor spot which showed up large on the attached image above and to the left of the Goldfinch's head as you can see.
This wasn't dust as using my Rocket blower and visible dust static brush failed to remove it. I did a wet clean and as expected it smeared on the first clean. When that happens I've been instructed to clean again with a new swipe. This time it disappeared. Guess it was an oil spot as I am very careful when changing lenses to tilt the camera forwards.